View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Jagiellonian Univeristy Repository Review Heme oxygenase-1 (HO-1, encoded by HMOX1) through degradation of pro-oxidant heme into carbon mon- Heme oxygenase inhibition in oxide (CO), ferrous ions (Fe2+) and biliverdin, exhibits cytoprotective, anti-apoptotic and anti-inflammato- cancers: possible tools and targets ry properties. All of these potential- ly beneficial functions of HO-1 may play an important role in tumors’ development and progression. More- over, HO-1 is very often upregulated Paulina Podkalicka1*, Olga Mucha1*, Alicja Józkowicz1, Józef Dulak1,2, in tumors in comparison to healthy Agnieszka Łoboda1,2 tissues, and its expression is further induced upon chemo-, radio- and photodynamic therapy, what results 1Department of Medical Biotechnology, Faculty of Biochemistry, Biophysics and in decreased effectiveness of the Biotechnology, Jagiellonian University, Krakow, Poland treatment. Consequently, HO-1 can be 2Malopolska Centre of Biotechnology, Jagiellonian University, Krakow, Poland proposed as a therapeutic target for * Equal contributions. anticancer treatment in many types of tumors. Nonetheless, possibilities of specific inhibition of HO-1 are strongly limited. Metalloporphyrins are widely Biological functions of HO-1 – an overview used in in vitro studies, however, they Heme, an organic cofactor composed of iron and organic part called pro- are unselective and may exert seri- toporphyrin IX, serves as a prosthetic group of many proteins. Hence, it facil- ous side effects including an increase in HMOX1 mRNA level. On the oth- itates a wide variety of processes like electron transport (cytochrome P450 er hand, detailed information about family), enzyme catalysis (e.g. peroxidase, catalase, cyclooxygenase, nitric pharmacokinetics and biodistribution oxide synthase) and reversible binding of gases (hemoglobin, myoglobin, of imidazole-dioxolane derivatives, guanylate cyclase). Furthermore, it is involved in regulation of protein syn- other potential inhibitors, is lacking. thesis and cells differentiation [1]. From the other hand, free heme released The genetic inhibition of HO-1 by RNA from intracellular hemeproteins causes cellular and tissue damage. Toxic interference (RNAi) or CRISPR/Cas9 and pro-oxidant properties of heme are the consequences of iron-depen- approaches provides the possibility to specifically target HO-1; however, dent reactive oxygen species (ROS) generation, lipids peroxidation and dis- the potential therapeutic application ruption of cellular membranes. As the result, an excessive level of circulating of those methods are distant at best. heme leads to several pathologies [2]. In summary, HO-1 inhibition might To overcome deleterious properties of heme, cellular machinery is be the valuable anticancer approach, equipped with heme oxygenases (HO), a microsomal enzymes which are re- however, the ideal strategy for HO-1 sponsible for the first, rate-limiting step in heme degradation pathway. The targeting requires further studies. enzyme cleaves heme into three biological active products: carbon monox- 2+ Key words: HO-1 inhibitors, siRNA, ide (CO), ferrous ions (Fe ) and biliverdin, which is subsequently converted CRISPR/Cas9, anticancer strategy, tu- into antioxidant bilirubin by biliverdin reductase. Molecular oxygen, cyto- morigenesis. chrome P450 reductase, and NADPH are required for the complete reaction [3]. So far, three isoforms of HO have been described – HO-1, HO-2 and HO-3; however, the latter is rather the pseudogene originated from HO-2 Contemp Oncol (Pozn) 2018; 22 (1A): 23–32 DOI: https://doi.org/10.5114/wo.2018.73879 transcript and was identified only in rats [4]. Although both HO-1 (encoded by HMOX1 gene) and HO-2 (encoded by HMOX2 gene) catalyze the same reaction in heme degradation pathway and share approximately 40% ho- mology, they differ in various aspects, including the kinetics of catalyzed reaction and the level of their expression in selected tissues. Finally, what is the most important, HO-2 is a constitutive isoform, whereas HO-1 – induc- ible. According to that, HO-1 is strongly upregulated in response to a wide spectrum of stimuli such as its substrate heme, proinflammatory cytokines, ROS, nitric oxide (NO), metalloporphyrins, heavy metals, prostaglandins, UV irradiation and many others. At the molecular level, expression of HO-1 is mainly activated by the transcription factor Nrf2 (nuclear factor erythroid 2-related factor-2). Certain stimuli cause the release of Nrf2 from its inhib- itor, Keap-1 (Kelch-like associating protein 1) and this lead to translocation of Nrf2 to the nucleus where it binds to antioxidant response element (ARE) located within the promoter of theHMOX1 gene. Moreover, several other transcription factors (e.g. AP-1, STAT and NF-κB) may be responsible for the induction of HO-1 expression in stressful conditions, such as oxidative stress (reviewed in: [5, 6]). Thus, except degradation of pro-oxidant heme, HO-1 exerts much broad- er and pleiotropic functions mediated by the end products of its activity. Carbon monoxide (CO) is a gasotransmitter which among several functions 24 contemporary oncology activates soluble guanylate cyclase (sGC) and cause va- from tissue injury, however these functions are tissue-spe- sodilation and inhibition of platelet aggregation. Through cific (reviewed in [6]). Moreover, its positive effect on an- modulation of MAPK (mitogen-activated protein kinases) giogenic activity of endothelial and vascular smooth cells pathways, it exerts anti-inflammatory functions: decreas- has been described [7, 8]. Ferrous ions increase the expres- es leukocyte adhesion, inhibits pro- and increases anti-in- sion of ferritin, which is responsible for iron sequestration, flammatory cytokines. Additionally, CO possess anti-prolif- hence it prevents toxicity caused by production of hydrox- erative and anti-apoptotic properties leading to protection yl radicals. Additionally, Fe2+ ions induce iron transporter (Fe-ATPase) responsible for iron efflux. Finally, biliverdin and bilirubin possess anti-oxidant and anti-inflammato- Photodynamic therapy ry properties by scavenging ROS, decreasing membrane lipids peroxidation, and inhibiting complement cascade (reviewed in: [6]). Gene polymorphism Chemotherapy HO-1 Emergent role of heme oxygenase-1 (HO-1) in cancer cells in tumor biology Oncogenes Radiotherapy Unfortunately, all of the above mentioned cytoprotec- tive actions of HO-1 and its by-products can be harmful, es- pecially when translated into pathophysiological process- pro-tumorigenic anti-tumorigenic es like tumorigenesis. Expression of HO-1 is significantly elevated in tumors, in comparison to healthy tissues, in- cluding pancreatic cancer, melanoma, renal cell carcinoma Proliferation Survival and others (reviewed in [9]). Noteworthy, expression of • Breast cancer • Breast cancer Angiogenesis HO-1 can be further enhanced by anticancer therapies (in- • Prostate cancer Metastasis • Prostate cancer • Pancreatic cancer Sensitivity to • Lung cancer cluding radio-, chemo- and photodynamic therapy) what • Lung cancer anticancer treatment ... • Hepatoma often results in decreased effectiveness of the treatment ... [10–12] (Fig. 1). It has to be stressed that the increased expression of Modulation of HO-1 as potential anticancer treatment HO-1 is found predominantly, but not only, in tumor cells Fig. 1. HO-1 as a target for anticancer therapy. HO-1 expression in (Fig. 2). Already in 1999, Nishie et al. have demonstrated tumor tissues is increased as a consequence of oncogenic transfor- the association of HO-1 with infiltrating macrophages and mation, modified by HO-1 promoter polymorphism, and further up- vascular densities in human gliomas [13]. HO-1 expres- regulated in response to anticancer therapies. Generally, HO-1 exerts sion in the stromal macrophages has been also shown in pro-tumorigenic effects through an increase in proliferation, surviv- al, and angiogenesis. However, also the opposite, inhibitory effect on the other cancer tissues. HO-1 expressed in FAP+/CD45+ the progression of tumors have been reported in some tumor types inflammatory macrophages with a M2 phenotype was demonstrated to play a crucial role in immune suppres- Expression of HO-1 in tumors sion [14]. Moreover, HO-1-specific regulatory CD8+ T cells were detected both in peripheral blood of cancer patients Tumor cells and among tumor-infiltrating lymphocytes in situ of can- HO-1 • Resistance to anticancer treatment cer patients [15]. HO-1-specific Treg cells were able to sup- HO-1 • Cancer progression HO-1 press immune response against cancer cells and efficiently HO-1 HO-1 inhibited T cell responses, including cytokine release, pro- HO-1 Immune cells liferation and cytotoxicity [15]. Interestingly, in melanoma, HO-1 was almost exclusively expressed in macrophages Macrophages and the negligible expression was found in the tumor cells and other stromal cell types [16]. Subcellular localization Treg cells One important aspect of HO-1 effect on tumor biology • Mostly cytoplasmatic • Modulation of tumor might be related to its cellular localization. Generally, HO-1 microenvironment • Truncated, nuclear form related • Suppression of immune response localizes mainly in the cytoplasm where it is associated to higher progression of cancer against cancer with endoplasmic reticulum (ER), caveoli or mitochondria • Mechanism not fully • Cancer progression understood [17]; however,